EP0046347A1

EP0046347A1 - Method of modifying starch

Info

Publication number: EP0046347A1
Application number: EP81303525A
Authority: EP
Inventors: George Henri Albert Marquette
Original assignee: PRODUITS DU MAIS Ste; PRODUITS DU MAIS SOC D; Produits Du Mais Ste; Unilever Bestfoods North America
Current assignee: PRODUITS DU MAIS Ste; Unilever Bestfoods North America
Priority date: 1980-08-07
Filing date: 1981-07-31
Publication date: 1982-02-24
Also published as: KR840001972B1; RO82683A; PL128502B1; ES8302101A1; YU192681A; DE3168630D1; ES504592A0; ZA815023B; PT73486A; ATE11548T1; DD201800A5; PH19133A; AU545028B2; JPS5753501A; EP0046347B1; FI812437L; KR830006395A; PT73486B; DK349981A; PL232532A1

Abstract

A preferably continuous process for gelatinising and chemically modifying starch comprises; providing an aqueous slurry of starch and gelatinising the starch therein; mixing the starch with a reagent therefor and subjecting the mixture, during or after gelatinisation, to ultra-high frequency radiation (preferably 2450 MH_z) to chemically modify the starch. The starch may be subjected to the radiation, e.g. under the conditions of gelatinisation or after application of a starch glue to a paper sheet.

Description

Our co-pending British Patent Application, No. 8013830 provides a method of chemically modifying starch by subjecting a mixture of starch with a modifying reagent to the action of ultra high frequency (UHF) radiation. The present invention is concerned with an application of that method to prepare glues and pastes, for example of the kind used in the paper and cardboard industry.
It is well-known that the preparation of chemically modified starch glues is usually done by subjecting a slurry of starch, already chemically modified by known methods, to a thermo-chemical or enzymatic thermal cooking in batch or by the use of continuous cookers as already known, in order to obtain the desired viscosities for different applications. This known process has the disadvantage of involving two steps, which are normally carried out in different factories.
The present invention provides a process for chemically modifying starch, comprising the steps of:-(a)(i) providing an aqueous slurry of the starch and then

(a)(ii) gelatinising the starch in said slurry;
(b)(i) forming a mixture of the said starch with at least one reagent which reacts chemically with the starch and then
(b)(ii) subjecting the resulting starch/reagent mixture to UHF radiation so as to effect chemical modification of the starch,

The process is preferably operated continuously. However, when an enzymatic cooker is used to gelatinise the starch, it may be convenient to use a batch or a continuous cooker.
Figures 1 to 6 of the accompanying drawings are all diagramatic representations of equipment for performing different variations of the process.
In each of the drawings, like numerals denote like parts.
Referring to Figure 1, a tank 10 to contain an aqueous starch slurry is provided with an inlet 16 for starch, and inlet 18 for a reagent to react chemically with the starch, and an inlet 20 for a catalyst. A volumetric pump 22 leads the aqueous slurry to a thermal cooker 24 which is also supplied with steam via a line 26. In the cooker 24 the starch is heated under pressure to a temperature of 130°C to 150°C and gelatinized.
The aqueous paste of gelatinized starch and reagent passes via a line 30 along a glass pipe (not shown) extending through a tunnel 32 forming a cavity for UHF radiation. The treated paste passes through a retention coil 34 whose exit is provided with a counterpressure valve 36 upstream of which is a line 38 connected to the steam line 26 for regulating the temperature of the system. Downstream of the valve 36, an exit conduit 40 is provided with a dilution water inlet 42 and connected to an expansion cyclone 44 which provides glue or paste ready for use.
In this variant of the process, the reagent and catalyst are added to the starch before gelatinisation. Gelatinisation is effected at elevated temperature and pressure, and the resulting paste is subjected, whilst still hot and under pressure, with the UHF radiation treatment. In this variant, therefore, step (b)(i) is performed before step (a)(ii), and step (b)(ii) is performed after step (a)(ii).
Referring now to Figure 2, the thermal cooker 24 has been omitted, and the UHF radiation treatment 32 serves not only to modify the starch but also to gelatinize it. The process is operated at atmospheric or elevated pressure, depending on the viscosity it is desired to obtain. This variant of the process is generally not preferred, on the ground that it is generally cheaper to heat the starch slurry to gelatinising temperature by means of steam than by UHF radiation. In this variant of the process, step (b)(i) is performed before step (a)(ii), and step (b)(ii) is performed during step (a)(ii).
The arrangement of Figure 3 resembles that of Figure l,except that the reagent 18 and the catalyst 20 are introduced into the system, not at the tank 10, but at the line 30, downstream of the thermal cooker 24 and immediately upstream of the UHF radiation tunnel 32. The starch paste is at this point at high temperature and pressure. The reagent and catalyst accordingly have to be introduced under high pressure, and this is generally not preferred. No particular advantage is gained by introducing the reagent and catalyst after, rather, than before gelatinisation. In this variant of the process, both of steps (b)(i) and (b)(ii) are performed after step (a)(ii).
The variant shown in Figure 4 is similar to that of Figure 3, in that the reagent 18 and catalyst 20 are introduced to the system at the line 30 immediately upstream of the UHF radiation tunnel 32. In Figure 4, the thermal cooker has been replaced by an enzymatic cooker 25. The starch and enzyme are introduced, via lines 16 and 17 respectively, into the tank 10, and the resulting slurry is led via a volumetric pump 22 and a steam heater 23 to the enzymatic cooker 25 which operates at a temperature of 80° to 90°C. When the slurry is at atmospheric pressure, there is no difficulty about adding the reagent and the catalyst to it. In this variant of the process, both of steps (b)(i) and (b)(ii) are performed after step (a)(ii).
In the variant shown in Figure 5, the starting starch is added to the tank 10, cooked in the cooker 24, and the resulting paste is diluted via water inlet 42 and passed to the expansion cyclone 44. The reagent 18 and catalyst 20 are added to a stream 46 of glue or paste which emerges from the expansion cyclone 44. The resulting mixture is applied to paper or cardboard 48, and the treated sheet subjected to UHF radiation in the tunnel 32. In this case, the UHF radiation performs the double function of drying the paper or cardboard and of inducing chemical reaction between the starch and the reagent. In this variant, both of steps (b)(i) and (b)(ii) are performed after step (a)(ii).
The variant shown in Figure 6 is similar to that of Figure 5, except that the reagent and catalyst are added to the tank 10, i.e. prior to cooking, instead of to the paste or glue in line 46. Again, it is the paper or cardboard sheet 48 carrying the glue or paste, rather than the glue or paste in bulk immediately after cooking, that is subject to the UHF radiation. In this variant of the process, step (b)(i) is performed before step (a)(ii) and step (b)(ii) performed after step (a)(ii).
The nature of the starch used is not critical. Suitable starches include corn starch, potato starch, wheat starch, tapioca starch, rice starch, sorghum starch, waxy corn starch and waxy sorghum starch. The starch may be in admixture with other materials, for example in the form of flour. The starting starch may optionally have been already chemically or physically modified or degraded. For example, it may be convenient in some cases to use acid thinned starch as the starting material..
Suitable reagents for chemically modifying starch according to the invention are well known. Examples are reagents which effect etherification, esterification, hydrolysis, cross-linking and oxidation, as described in Radley "Starch and its Derivatives," 1968 Chapman and Hall Ltd., Chapters 11 and 12; and Whistler/Pascall "Starch: Chemistry and Technology" Academic Press, Volume 1 (1965) Chapters 18 and 19, and Volume II (1967) Chapters 9,10,11,13,14,15,16,17 and 19. It is also possible to prepare starch copolymers and starch graft copolymers, for example with products from the classes polyvinyl alcohols, acrylamides and monomers and polymers derived from petroleum.
The amount of the reagent used depends on the degree of substitution required,and on the reaction efficiency.
UHF radiation has a frequency in the range 300 MHz to 300,000 MHz. Within this range, only certain specific bands are permitted for industrial use in many countries, and these include 915, 2450, 5800 and 22155 MHz.
It is preferred to use UHF radiation of a frequency which activates the H-OH dipoles of the starch. The frequency of industrial UHF apparatus built today corresponding best to the dielectric constant of the H-OH dipoles of starch is 2450 MHz. In this alternating electromagnetic field, the H-CH dipoles orient themselves and are thereby subjected to a permanent oscillation : which activates them. In this way the chemical reactions can be induced immediately.
The time for which it is necessary to subject the mixture to UHF radiation in order to achieve the desired degree of chemical modification depends on the power available and the flow rate of the starch slurry or paper or. cardboard sheet carrying the starch glue.
Generally speaking, to induce a chemical reaction the processing time under the UHF radiation is not more than five minutes, and is quite often loss than one minute. The temperature increase caused by UHF radiation is often less than 50°C, and is in any event less than 100°C.
The nature of the equipment used to effect the radiation treatment is not critical. Conveniently, this equipment includes a transmitter, a tunnel constituting a wave guide and means for conveying the starch/reagent mixture to be treated through the tunnel, the form and size of the wave guide being calculated in relation to the product to be processed and the frequency of the radiation used. (Such equipment is offered by Industrie Microondes Internationale under the Trade Mark Gigatron). When the mixture is in slurry form, the conveying means may comprise a pipe or trough of a material transparent to the UHF radiation, for example glass.

EXAMPLE 1

The following example of a method according to the invention was performed in equipment as shown in Figure 1.
There was continuously prepared an aqueous slurry of native corn starch at a dry solid content of 25% by weight, which contained in addition a cationic reagent (epoxypropyltrimethylammonium chloride) in an amount of 53 kg of active material per ton of dry starch, and a catalyst (8% aqueous solution of sodium hydroxide) in an amount of 18 kg of sodium hydroxide per ton of dry starch.
The mixture thus prepared was passed to a cooker where the starch was gelatinised by the injection of steam at 700 kPa and the temperature raised to 130°C. The resulting paste was passed at 360 litres per hour through a tube where it was subjected to UHF radiation (2450 MH_z3000 W) for twenty seconds.
The degree of substitution evaluated on the basis of a glue sample previously neutralised and dialysed in order to eliminate all constraining solubles (reagents which did not react) was 0.054.

EXAMPLE 2

This was performed in equipment shown in figure No.2. In this case UHF radiation serves not only to modify the starch but also to gelatinise it.
To show the flexibility of the process an acid thinned corn starch was used for this example. That means a low viscosity of the paste, and a temperature of cooking of about 100°C without any pressure.
As for Example No. 1 an aqueous slurry of starch at a dry solids content of 25 % by weight was continuously prepared.
To this acid thinned corn starch slurry were added a cationic reagent (epoxypropyltrimethylammonium chloride) in an amount of 53 kg of active material per ton of dry starch, and a catalyst (8 % aqueous solution of sodium hydroxide) in an amount of 18 kg of sodium hydroxide per ton of dry starch.
This mixture was passed at 300 litres per hour through a tube where it was subjected to UHF radiation (2450 MH _z 30 kW) for one minute.
The degree of substitution evaluated on the basis of the glue sample previously neutralised and dialysed in order to eliminate all constraining solubles (reagents which did not react) was 0,035.
It was assumed that there took place, at the same time, the heating of the starch slurry and the chemical reaction (the temperature was below 80 C), and that the gelatinisation of the starch only took place subsequently.
It was also assumed that the reason why a lower degree of substitution was obtained than in Example lwas that the starch granules were not totally destroyed when the chemical reaction took place.

EXAMPLE 3

This example was performed in equipment as shown in Figure 3.
The conditions used were those of Example 1 but in order to achieve good mixing of the chemicals into the paste, acid thinned corn starch was used in the place of native corn starch (the viscosity was lower).
An aqueous slurry of acid thinned corn starch (scott 60 g = 45 s) as a dry solids content of 25% by weight was continuously prepared. This slurry was passed to a cooker where the starch was gelatinised by the injection of steam at 700 kPa and the temperature raised to 130°C.
To the resulting paste were added, under pressure, cationic reagent (epoxypropyltrimethylammonium chloride) in an amount of 53 kg of active material per ton of dry starch, and a catalyst (8% aqueous solution of sodium hydroxide) in an amount of 18 kg of sodium hydroxide per ton of dry starch.
The mixture was then passed through a tube where it was subjected to UHF radiation at 36 litres per hour (2450 MH_z 600 W) for forty five seconds).
The degree of substitution evaluated on the basis of a glue sample previously neutralised and dialysed in order to eliminate all constraining solubles (reagents which did not react) was 0.050.

EXAMPLE 4.

This Example was performed in equipment shown in Figure 4.
First an aqueous slurry of native corn starch at a dry solids content of 25% by weight, and at 6.2/6.5 pH was continuously prepared. To this slurry were added, 0,01% of alpha amylase enzyme (1800 units per gramme) and 200 p.p.m. of calcium as calcium carbonate based on dry starch. This enzyme was added to hydrolyse the starch using a well known technique hereafter described.
The starch slurry with enzyme and calcium carbonate was passed through a hydro-heater where the starch was gelatinised by injection of steam at 500 kPa and the temperature raised to 90°C. The resulting paste was then passed through a column in which the hydrolysis took place, the temperature was maintained at 90 C. The hydrolysis time was about 35 minutes.
After this operation, the starch paste had a very low viscosity (below 100 mPas) and the addition of chemicals was easier. So to this starch paste were added cationic reagent (epoxipropyltrimethylammonium chloride) in an amount of 53 kg of active material per ton of dry starch, and a catalyst (8% aqueous solution of sodium hydroxide) in an amount of 18 kg of sodium hydroxide per ton of dry starch.
At this point the mixture was subjected to UHF radiation at 360 litres per hour through a glass tube (2450 MH_z 3000 W.) for thirty seconds.
The degree of substitution evaluated on the basis of a glue sample previously neutralised and dialysed in order to eliminate all constraining solubles (reagents which did not react) was 0.050.

EXAMPLES 5 and 6

According to figures 5 and 6 modification of starch could be realised directly during the paper sizing using UHF radiation.
The starch pastes were prepared as described in examples 1 and 3.
According to figure 5 native corn starch or acid thinned corn starch slurry prepared continuously was passed through a cooker where the starch was gelatinised by the injection of steam at 700 kPa and the temperature raised to 130°C. To this paste (after dilution if it is necessary for sizing application) were added chemicals; cationic reagent (epoxypropyltrimethylammonium chloride) in an amount of 15 kg of active material per ton of dry starch, and a catalyst (8% aqueous solution of sodium hydroxide) in an amount of 16 kg of sodium hydroxide per ton of dry starch.
According to figure 6 native corn starch or acid thinned corn starch slurry prepared continuously was mixed with chemicals; cationic reagent (epoxypropyltrimethylammonium chloride) in an amount of 15 kg of active material per ton of dry starch, and a catalyst (8% aqueous solution of sodium hydroxide) in an amount of 16 kg of sodium hydroxide per ton dry starch. This mixture was then passed through a cooker where the starch was gelatinised by the injection of steam at 700 kPa and the temperature raised to 130°C.
At this point and in both cases a mixture of starch paste, chemicals, reagent, catalyst was obtained.
This mixture was used to size paper sheets using a coating rod technique which is well known and is not critical. The wet sized paper sheets were then subjected to UHF radiation. In this case the UHF radiation performs the double function of drying the paper and inducing chemical reaction between the starch and reagents.
Three sheets each measuring 20 cm x 30 cm and having about 5 gm/m² of dry substance coating were subjected to UHF radiation (2450 MH , 300 W) for one minute. The degree of substitution was evaluated after repulping sized paper sheet, and filtration, neutralisation and dialysis of the obtained solution in order to eliminate all constraining solubles (reagents which did not react). The degree of substitution obtained was 0,015.

Claims

1. A process for chemically modifying starch, comprising the steps of:-

(a)(i) providing an aqueous slurry of the starch and then

(a)(ii) gelatinising the starch in said slurry;

(b)(i) forming a mixture of the said starch with at least one reagent which reacts chemically with the starch and then

(b)(ii) subjecting the resulting starch/reagent mixture to UHF radiation so as to effect chemical modification of the starch,

step (b)(i) being performed before or after step (a)(ii), and step (b)(ii) being performed during or after step (a)(ii).

2. A process as claimed in claim 1, which process is operated continuously.

3. A process as claimed in claim 2, which process comprises providing an aqueous slurry of starch in admixture with at least one reagent which reacts chemically with the starch, effecting gelatinisation of the starch at elevated temperature and pressure, and subjecting the resulting paste, while still hot and under pressure, to UHF radiation so as to effect chemical modification of the starch.

4. A process as claimed in claim 2, which process comprises providing an aqueous slurry of starch in admixture with at least one reagent which reacts chemically with the starch, and subjecting the resulting starch/reagent mixture to UHF radiation so as to effect gelatinisation of the starch and chemical modification of the starch.

5. A process as claimed in claim 2, which process comprises providing an aqueous slurry of starch, gelatinising the starch in said slurry under elevated temperature and pressure, introducing into the starch slurry at least one reagent which reacts chemically with the starch, and then subjecting the resulting starch/reagent mixture, still at elevated temperature and pressure to UHF radiation so as to effect chemical modification of the starch.

6. A process as claimed in claim 1 or claim 2, which process comprises providing an aqueous slurry of starch, enzymatically gelatinising the starch in said slurry, forming a mixture of the gelatinised starch with at least one reagent which reacts chemically with the starch, and then subjecting the resulting starch/reagent mixture to UHF radiation so as to effect chemical modification of the starch.

7. A process as claimed in claim 2, which process comprises providing an aqueous slurry of starch, gelatinising the starch in said slurry, forming a mixture of the said gelatinised starch with at least one reagent which reacts chemically with the starch, applying the resulting mixture to a sheet and subjecting the treated sheet to UHF radiation so as to effect chemical modification of the starch.

8. A process as claimed in claim 2, which process comprises providing an aqueous slurry of starch in admixture with at least one reagent which reacts chemically with the starch, gelatinising the starch in said slurry, applying the resulting paste to a sheet, and subjecting the treated sheet to UHF radiation so as to effect chemical modification of the starch.

9. A process as claimed in any one-of claims 1 to 8, wherein the starch used is corn starch.

10. A process as claimed in any one of claims 1 to 9, wherein the reagent which reacts chemically with the starch is an etherification, esterification, hydrolysis, cross-linking, oxidation or dextrinisation reagent.

11. A process as claimed in any one of claims 1 to 10, wherein the UHF radiation has a frequency of about 2450 MHz. '12. Starch which has been chemically modified by the process of any one of claims 1 to 11.